Golang: Struct

By Xah Lee. Date: . Last updated: .

Struct is user-defined type. It defines a collection of “fields”, each field is a name and a value of a specific type.

Struct is similar to golang map, or python dictionary, ruby hashtable, JavaScript object, except that number of keys and key names are fixed, predefined, as a user-created type.

Once you defined a struct type (with a given name), you can create struct of that name.

Note, struct is very important in golang. because methods, and interface, are based on it.

Define a New Struct Type

Here's how to define a struct.

type Name struct { name1 type1 name2 type2 … }

here's how to create a struct you just defined:

struct_name{val1, val2 …}

or

struct_name{name1:val1, name2:val2 …}

package main

import "fmt"

// define a struct named PP
type PP struct {
    x int
    y int
}

func main() {
    // create a struct PP
    var x PP = PP{1, 2}

    // print struct with value only
    fmt.Printf("%v\n", x) // {1, 2}

    // print struct with field name and value
    fmt.Printf("%+v\n", x) // {x:1 y:2}
}

Create Struct: Struct Literals

A struct literal lets you create a value of a given struct type.

For example, if you have this struct type

type PP struct{ x, y int }

you can create a value by

var p1 = PP{x:3, y:4}

or

var p1 = PP{}

and use PP.x=3 etc to fill the field values later.

package main

import "fmt"

// define a struct type
type PP struct{ x, y int }

func main() {

    // create a struct of PP
    var p1 = PP{x: 3, y: 4}

    fmt.Printf("%#v\n", p1) // main.PP{x:3, y:4}

}

If a key is omitted, it defaults to its zero value.

[see Zero Value]

package main

import "fmt"

type PP struct{ x, y int }

func main() {
    var p1 = PP{y: 4}
    fmt.Printf("%#v\n", p1) // main.PP{x:0, y:4}
}

Alternatively, you can omit keys and only use values.

var p1 = PP{3, 4}

If you omit keys, the order must be the same as the struct type is defined, and none of element must contain a key.

package main

import "fmt"

type PP struct{ x, y int }

func main() {
    var tt = PP{3, 4}
    fmt.Printf("%#v\n", tt) // main.PP{x:3, y:4}
}

Get/Set Field Value

Struct fields are accessed using a dot.

package main

import "fmt"

type PP struct {
    x int
    y int
}

func main() {

    v := PP{3, 4}

    // get a field value
    fmt.Println(v.x) // 3

    // set a field value
    v.x = 4
    fmt.Println(v.x) // 4
}

Print Struct

[see Golang: Print]

Pointer to structs

[see Pointer]

Reference

The Go Programming Language Specification - The Go Programming Language#Struct_types

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Golang

  1. Compile, Run
  2. Package, Import
  3. Comment
  4. Print
  5. String
  6. Rune
  7. Variable
  8. Zero Value
  9. Constant
  10. If Then Else
  11. Switch/Case
  12. Loop
  13. Basic Types
  14. Array
  15. Slice
  16. Map
  17. Struct
  18. Function
  19. regexp
  20. Read File
  21. Write to File
  22. Walk Dir
  23. Check File Exist
  24. System Call
  25. Pointer
  26. Defer
  27. Random Number

Examples

  1. Validate Links
  2. Generate Sitemap

Reference

  1. Go Spec